In certain laser installations, microstructures are created according to the mask projection technique, as e.g. disclosed in WO 2007/012215 to the applicant of the present invention. The laser may e.g. be a KrF excimer laser having a wavelength of 248 nanometers (nm). The mask projection technique implemented with such laser installations requires a mask and diaphragm combination that may be arranged in a changer device.
A mask serves for shaping a predetermined intensity profile of the laser beam and thus to transmit the laser beam in certain portions of the mask surface only. Consequently, when irradiated with a high-energy laser, it is subject to high stresses that may lead to deformations and to high wear. To prevent that laser radiation may pass through the non-transmitting areas of the mask surface, there are the following possibilities: Absorption, reflection, or scattering.
For the first possibility, a lacquer coat may be applied in these areas, but it will not withstand the stress for long. The same applies to optical lithography. For the second possibility, e.g. a dielectric mirror may be deposited in the desired locations. However, this technique is very demanding.
For producing scattering areas, etching techniques are known in the art today, but these are far too inaccurate. The above-mentioned disadvantages apply especially if masks serve for creating e.g. optically effective diffraction gratings and similar microstructures. This severe drawback of a relatively coarse forming of areas with less transparency applies also to the roughening of surfaces according to JP 2002-011589 A which are produced by sandblasting.